Piston engine aircraft exhaust system

ABSTRACT

An exhaust system for an aircraft piston engine having a crankcase, the system comprising an efficient exhaust pipe stack in fluid communication with a venturi which provides a vacuum to an air oil separator and to the engine crankcase.

FIELD OF THE INVENTION

The present invention relates to exhaust systems for aircraft powered by piston engines. More particularly, the present invention relates to an exhaust system having a vacuum design for improved performance and air/oil separation and which is particularly well adapted for use on Beech Bonanza and Beech Baron aircraft.

BACKGROUND OF THE INVENTION

Many smaller airplanes are powered by piston engines. These engines are designed to be lightweight and efficient but are notorious for venting engine oil outboard- usually onto the belly of the aircraft. There remains room for improvement in this regard and there remains room for improvement with respect to engine efficiency.

Also, over the past years aircraft engines have become increasingly expensive. There are only a few manufacturers of new piston engines for aircraft and there is little economy of scale as well as expense factors relating to weight, safety, government regulations. All leading the industry to high costs. Accordingly, many older engines are maintained in service, at least in part because replacement costs are so high. Many engines have been overhauled several times to be maintained in service. Thus, it is believed there is a need for add-on systems which can be added on to already existing engines as well as incorporated into the manufacture of new engines to improve engine performance and to improve separation of oil from aircraft engine crankcase venting for return to the engine crankcase.

Accordingly, the present invention provides an improved exhaust system which can be added onto an existing engine or incorporated into the manufacture of a new engine. The system of the present invention provides a tuned or semi-tuned exhaust stack resulting in higher horsepower due to an improved exhaust flow path. A venturi is provided in the exhaust system to provide a vacuum source for an air oil separator and for the crankcase. The vacuum feature of this invention is used to enhance air oil separation in an air oil separator which removes oil from the crankcase vent for return to the engine crankcase oil sump. The engine having an exhaust of this invention will be smoother running due to even intake charge distribution instead of uneven distribution due to varying exhaust pressures during valve overlap. This in turn results in more even and lower cylinder head temperatures because of more even exhaust back pressure from cylinder to cylinder.

These and other advantages of the present invention will be appreciated by those skilled in the art from the following specification and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a somewhat diagrammatic illustration of a preferred embodiment of an exhaust system of the present invention shown in combination with an associated piston engine for an aircraft.

SUMMARY OF THE INVENTION

An exhaust system for an aircraft piston engine having a crankcase, the system has an efficient exhaust stack in fluid communication with a venturi which provides a vacuum to an air oil separator and to the engine crankcase.

DESCRIPTION OF THE INVENTION

Now referring to FIG. 1, a preferred embodiment of an exhaust system of the present invention is shown and indicated generally by the numeral 10. Exhaust system 10 is shown in association with a Beech Bonanza aircraft engine 12 which has three cylinders 14 on each side as is typical of a light aircraft piston engine. Broadly speaking exhaust system 10 comprises exhaust pipe stacks 16 and 18, venturies 20 and 22, check valve 24 and air oil separator 26.

Exhaust pipe stacks 16 and 18 have exhaust flanges 28, each of which is for connection to an appropriate exhaust port of a cylinder 14. It is preferred that each exhaust pipe stack be designed as a tuned exhaust for increased horsepower due to the lower back pressure of a tuned exhaust. However, the reality of exhaust pipe design for aircraft engines is that the system must fit within a close cowling, in which case a fully tuned exhaust may not be practicable although one should seek as efficient a flow as is practicable.

Exhaust pipe stack 16 is connected to venturi 20 so that exhaust flowing through pipe stack 16 from engine 12 flows through venturi 20 as indicated by arrow 32. Exhaust pipe stack 18 is connected to venturi 22 in similar fashion so that exhaust flows through pipe stack 18 and through venturi 22 as indicated by arrow 34. The exhaust streams exit through venturies 20 and 22 as indicated by arrows 36 and 38. Exhaust flow through Venturi's 20 and 22 induce a vacuum condition or reduced pressure condition as a result of the well-known Venturi effect of gaseous flow through a reduced diameter conduit. The vacuum from Venturi 20 is connected by hose 40 to check valve 24. The vacuum from Venturi 22 is connected by hose 42 to check valve 24. Check valve 24 is connected by hose 44 to air oil separator 26. Lower pressure or vacuum is drawn towards venturies 20 and 22 as indicated in the direction shown by arrows 46, 48 and 50. Check valve 24 prevents from flow in the opposite direction which might occur, for example, after engine shut down.

Air oil separator 26 can be a conventional air oil separator as his commonly used in the aircraft industry and serves to remove oil from the vapors in the crankcase and return the removed oil to the oil sump. Air oil separator 26 is connected by hose 52 to crankcase vent 54. Oil separated from crankcase vented gases is returned through hose 58 to oil sump 60 to rejoin oil supply 62. Air oil separator 26 communicates vacuum to crankcase 56 thus reducing the amount of air resistance encountered by the pistons in cylinders 14 during the power stroke of each cylinder 14.

In operation, vacuum from venturies 20 and 22 is communicated to crankcase 56 through air oil separator 26 to reduce the air pressure in crankcase 56. This reduced pressure reduces aerodynamic forces on pistons and rotating parts in crankcase 56. Also, the reduced pressure, or vacuum, scavenges unwanted gases, contaminants and moisture from the crankcase. The engine enjoys higher horsepower, runs smoother due to more even intake charge distribution during valve overlap and more even cylinder head temperatures due to more even exhaust back pressure between cylinders. In summary, the exhaust system of the present invention provides improved engine performance as well as returning oil to the engine oil sump which would otherwise be lost through the engine crankcase vent.

While preferred embodiments of the present invention have been disclosed in the foregoing disclosure, the present invention is subject to variation and modification within the broad scope of the invention. For example, only one venturi or more than two venturies might be used with two exhaust pipe stacks. Such modifications are intended to be within the broad scope of this invention which is intended to be limited only by the scope of the following claims. 

What is claimed is:
 1. An exhaust system for an aircraft piston engine having a crankcase, the system comprising an efficient exhaust pipe stack in fluid communication with a venturi which provides a vacuum to an air oil separator and to the engine crankcase. 